Type Bangla in the following input boxes

Or type here

You can switch to English and Bangla anytime by pressing Ctrl+y in windows and linux (Command+y in mac)
Checkout the source code of BanglaInputManager plugin which acts as the central engine
Checkout the source code of Phonetic Input Driver which parses the input phonetically
Checkout the source code of Unijoy Input Driver which parses the input following unijoy keymapping